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Examples

This section presents a few unrelated examples of some aspects of asn1c usage.
[Example requested by Eyal Carmi]

Using the asn1c generated structures

Let's suppose we need to employ the following ASN.1 module:
MyModule.asn1
MyModule DEFINITIONS ::= BEGIN MyTypes ::= SEQUENCE { myObjectId OBJECT IDENTIFIER, mySeqOf SEQUENCE OF MyInt, myBitString BIT STRING { muxToken(0), modemToken(1) } } MyInt ::= INTEGER (0..65535) END
1. Compile this module into a set of .c and .h files with the following command line:
> asn1c MyModule.asn1
2. Create a .c file with the following contents:
my-program.c
#include <stdio.h> /* for stdout */ #include <stdlib.h> /* for malloc() */ #include <assert.h> /* for run-time control */ #include "MyTypes.h" /* Include MyTypes definition */ int main() { /* Define an OBJECT IDENTIFIER value */ int oid[] = { 1, 3, 6, 1, 4, 1, 9363, 1, 5, 0 }; /* or whatever */ /* Declare a pointer to a new instance of MyTypes type */ MyTypes_t *myType; /* Declare a pointer to a MyInt type */ MyInt_t *myInt; /* Temporary return value */ int ret; /* Allocate an instance of MyTypes */ myType = calloc(1, sizeof *myType); assert(myType); /* Assume infinite memory */ /* * Fill in myObjectId */ ret = OBJECT_IDENTIFIER_set_arcs(&myType->myObjectId, oid, sizeof(oid[0]), sizeof(oid) / sizeof(oid[0])); assert(ret == 0); /* * Fill in mySeqOf with a couple of integers. */ /* Prepare a certain INTEGER */ myInt = calloc(1, sizeof *myInt); assert(myInt); *myInt = 123; /* Set integer value */ /* Fill in mySeqOf with the prepared INTEGER */ ret = ASN_SEQUENCE_ADD(&myType->mySeqOf, myInt); assert(ret == 0); /* Prepare another integer */ myInt = calloc(1, sizeof *myInt); assert(myInt); *myInt = 111222333; /* Set integer value */ /* Append another INTEGER into mySeqOf */ ret = ASN_SEQUENCE_ADD(&myType->mySeqOf, myInt); assert(ret == 0); /* * Fill in myBitString */ /* Allocate some space for bitmask */ myType->myBitString.buf = calloc(1, 1); assert(myType->myBitString.buf); myType->myBitString.size = 1; /* 1 byte */ /* Set the value of muxToken */ myType->myBitString.buf[0] |= 1 << (7 - myBitString_muxToken); /* Also set the value of modemToken */ myType->myBitString.buf[0] |= 1 << (7 - myBitString_modemToken); /* Trim unused bits (optional) */ myType->myBitString.bits_unused = 6; /* * Print the resulting structure as XER (XML) */ xer_fprint(stdout, &asn_DEF_MyTypes, myType); return 0; }
3. Compile every .c file together:
> cc -o my-program.exe -I. *.c
4. Run it:
> ./my-program.exe
<MyTypes>
    <myObjectId>1.3.6.1.4.1.9363.1.5.0</myObjectId>
    <mySeqOf>
        <MyInt>123</MyInt>
        <MyInt>111222333</MyInt>
    </mySeqOf>
    <myBitString>11</myBitString>
</MyTypes>
[Reverse example requested by Eyal Carmi]

Fetching information from XER encoded data

Suppose we need to decode the XER data from the previous example and place its contents into a specific C types.

1. Compile the ASN.1 module from the previous example into a set of .c and .h files with the following command line:

> asn1c MyModule.asn1
2. Create a .c file with the following contents:
my-program.c
#include <stdio.h> /* for stdout */ #include <stdlib.h> /* for malloc() */ #include <assert.h> /* for run-time control */ #include "MyTypes.h" /* Include MyTypes definition */ int main(int argc, char *argv[]) { char buf[1024]; /* Hope, sufficiently large buffer */ MyTypes_t *myType = 0; asn_dec_rval_t rval; char *filename; size_t size; FILE *f; /* * Target variables. */ int *oid_array; /* holds myObjectId */ int oid_size; int *int_array; /* holds mySeqOf */ int int_size; int muxToken_set; /* holds single bit */ int modemToken_set; /* holds single bit */ /* * Read in the input file. */ assert(argc == 2); filename = argv[1]; f = fopen(filename, "r"); assert(f); size = fread(buf, 1, sizeof buf, f); if(size == 0 || size == sizeof buf) { fprintf(stderr, "%s: Too large input\n", filename); exit(1); } /* * Decode the XER buffer. */ rval = xer_decode(0, &asn_DEF_MyTypes, &myType, buf, size); assert(rval.code == RC_OK); /* * Convert the OBJECT IDENTIFIER into oid_array/oid_size pair. */ /* Figure out the number of arcs inside OBJECT IDENTIFIER */ oid_size = OBJECT_IDENTIFIER_get_arcs(&myType->myObjectId, 0, sizeof(oid_array[0]), 0); assert(oid_size >= 0); /* Create the array of arcs and fill it in */ oid_array = malloc(oid_size * sizeof(oid_array[0])); assert(oid_array); (void)OBJECT_IDENTIFIER_get_arcs(&myType->myObjectId, oid_array, sizeof(oid_array[0]), oid_size); /* * Convert the sequence of integers into array of integers. */ int_size = myType->mySeqOf.list.count; int_array = malloc(int_size * sizeof(int_array[0])); assert(int_array); for(int_size = 0; int_size < myType->mySeqOf.list.count; int_size++) int_array[int_size] = *myType->mySeqOf.list.array[int_size]; if(myType->myBitString.buf) { muxToken_set = myType->myBitString.buf[0] & (1 << (7 - myBitString_muxToken)); modemToken_set = myType->myBitString.buf[0] & (1 << (7 - myBitString_modemToken)); } else { muxToken_set = modemToken_set = 0; /* Nothing is set */ } return 0; }
3. Compile every .c file together:
> cc -o my-program.exe -I. *.c
4. Save the XER output from the step #4 of the previous example, and run the newly created binary against it:
> ./my-program.exe file.xer

The ASN.1 Compiler Copyright © 2003—2013 Lev Walkin <vlm@lionet.info>